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Astronomy 2021A/B
Peter G Brown

1 – A Universe of Life? (page 1) 1.1 THE POSSIBILITY OF LIFE BEYOND EARTH - Aliens everywhere in media – movies, tabloids, even serious papers/magazines run the occasional articles on UFO sightings or “Area 51” - Around ½ of all Americans claim to believe we have already been visited by beings from other worlds - Scientists skeptical about aliens on Earth .: search for life in other worlds, searching for signals - Important search to change perspective on how we fit into universe as a whole, and give deeper meaning to life here on Earth What are we searching for? - Extraterrestrial life (life beyond Earth) includes any sign of life – simple, complex, intelligent, whatever - Yet must define what life is in the first place, which affects how we search for life in universe  complicated question o e.g. beetle/mushroom vs clouds/fire/crystals o how do we classify? Movement, growth, reproduction and spread? Right side does this too o because of difficulty , for scientific search, “life” = recognizably Earth-like, can recognize based on studying Earth life  must start somewhere Is it reasonable to imagine life beyond Earth? - Search for life new; IDEA of life not  ancient cultures e.g. ancient Greeks - Until recently, no way to scientifically test, could only imagine o Any small data misinterpreted too - Venus thought paradise; mars thought canals .: martian life (none actually) - NOW enough telescope/spacecraft photos of our solar system .: quite confident no life  still looking though LOT. - Why? o 1) Tiny microbes might exist, even if multicellular don’t o 2) knew stars everywhere, now know planets everywhere too .: more places to look o 3) enough knowledge/tech to go about it scientific method  Know conditions life exist  Can’t look yet, but spacecraft improving and telescope for signs improving 1.2 THE SCIENTIFIC CONTEXT OF THE SEARCH - All fields involved in search for life  computation, computer simulation (stars, planets, molecules interactions) - 3 important o Astronomy o Planetary science  Geology  Atmospheric science o Biology How does astronomy help us understand the possibilities for extraterrestrial life? - Most of human history, universe conception very diff than now o Geocentric (Earth-centered) view of the Universe: all stars, planets revolve around Earth  Dominated for thousands of years - .: Astronomy is key  Earth regular planet revolving around regular star in context of VAST cosmos (.: lots potential life) o By studying distant objects, we’ve learned physical laws operate in rest of universe are same as those that operate on Earth o .: if something happens here, theoretically can happen elsewhere o .: we’re not special in any way How does planetary science help us understand possibilities for ET life? - Planetary science = study of almost everything related to planets o Planets, moons orbiting, how planets form, objects forming in association (comets, asteroids) - 2 important ways - 1) learning how planets form allows understanding of how common planets are o Otherwise how to know stars can have planets around them o  last half of 20 century, moon/planet evidence helped understanding of how our own solar system formed .: more likely stars similarly born with planets o 1995, first extrasolar planet (planets orbiting stars other than our Sun) discovered o Now a lot discovered  .: lots stars with planets .: lots possibilities of life - 2) help understand how planets work o E.g. compare planets  why some rocky, some gas (H and He)  Why venus so much hotter though barely closer to sun  Why moon desolate though same distance from sun  Why mars cold/dry now, but evidence that warmer/wetter before - Most importantly, helps us understand what to look for in search for habitable worlds – worlds that contain basic necessities for life o .: helps improve odds, reduces where to look to most promising POTENTIAL (not actual life, can’t tell yet) o Habitable = for microbes (since we started that way too), though might find larger too How does bio help us understand possibilities of ET life? - Can’t look for life if don’t know how life functions
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